Parabolic reflector with a structural member front skin



y 8,1958 J. L.,DARROUZET 2,842,767

- PARABOLIC REFLECTOR WITH A STRUCTURAL MEMBER FRONT SKIN Filed Feb. 5, 1954 2 Sheets-Sheet 1 INVENT OR ATTORNEYS vJuly 8, 1958 J. L. bARRouzET 2,842,767

PARABOLIC REFLECTOR WITH A STRUCTURAL MEMBER FRONT SKIN Filed-Feb. 3 1954 2 Sheets-Sheet 2 INVENTOR- ATTTNUVEYS back and forthlthr'ough an'arc ofle ss than 180. anantenna mounted thus, the reflector is subjected to considerable vibration as itreaches the end of its travel PARABOLIC REFLECTOR WITH A STRUCTURAL MEMBER FRONT SKIN IohnL. Darrouzet, Dallas, Tex., assignor to Texas Instruments Incorporated, Dallas, Tex., a corporation of Delaware 7 Application February 3, 1954, Serial No. 407,937

3 Claims. (Cl. 343-781) I This invention relates "generally to antennas suitable for the transmission of R. F. power and in particular to a structural member front 7 a parabolic reflector having skin.

radar, consists-mainly of two parts, the antenna feed 'An antenna of the scanning type, such as is used in ortermination'of thetransmission line for R. F. power and theparabolic reflector. Further, two forms of parabolic reflectors are used, the cylindrical parabolic reflector and paraboloids of revolution which may or may not follow a special contour. In this latter type of parabolic reflector, the transmission line terminates at the focal point of the parabola. The R. F. energy sprays out of this feed pointin thedirection of the reflector where the energy is directed outwardly in the form of a concentrated beam whichmay ormay not be symmetrical This beam upon striking some object along its'path is reflected back to thereflector Where the energy is again concentrated at the focal point or end point of the. transmission line. From there, the energy is transmittedto the receiving section of. the radar system by means well known in the art.; i

Some antennas are mounted for full rotation. The more common technique, however, particularly in airborne installations, isto mount the antenna'to oscillate \Vith arcand reverses direction which causes distortion of the parabolic reflecting surface. Another source of distortion in the reflector isthefrequericyof the vibrations generated by the power plant of the craft carrying the antenna. Thus assuming as an example a maximum engine speed 0153300 R. P .l\/i., the reflector will be sub; jected to severe vibration at some engine speed between 0 and 3300 R. P. M.'unless it is so reinforced structurally that'its resonant frequency is above 55 cps. To minimize this vibration and concomitant distortion, the practice has been to build a framework of structural sections and rivet this framework to the rear of the reflector. Following this practice does not produce the most fruitful results because of the large amount of time and expense required to construct the framework and attach same and the considerable weight added to the reflector. Further and as important, complete success has not been achieved in providing a structure with a sufiiciently high resonant frequency to prevent vibration and distortion.

flector support structure.

It is another object of this invention to provide a 'stilfener structure for a reflector that is considerably lighter in weight than structures previously used whereby to attain a saving in weight which willbe of particular benefit in airborne installations. 7

It is still afurther object of this invention to provide a reflector stiffener structure that is more simply and easily attached to the parabolic reflector and is less expensive than structures used heretofore.

Other objects and advantages willbecome apparent from a detailed consideration of the following description when taken in conjunction with the appended drawings in which: a

Figure 1 is a view in perspective illustrating the parabolic reflector and the structural member of this invention before assembly;

Figure 2 is a side view of the reflector and the structural member assembled and mounted on a standard support; a a

'Figure 3 is a front elevation view of the. reflector structurally reinforced in accordance with the present invention; and V t Figure 4 is a partial rear elevation view of the reflec tor and the waveguide transmission line to the reflector.

Referring now to Figure 1, the invention is illustrated in its most basicform. The reflector 10 is aconcave parabola as viewedrfrom the focal point side and is formed with a narrowflange 12 extending around the contour or periphery of the reflector. evenly spaced rivet holes 13 are drilled into flange 12 of reflector 10. Structural member 11, hereinafter termed the front skin, is concave, similar to reflector ltl'though not necessarily a parabola,,and, has a narrow flange-14 extending around its outside rim, and is the same in contour as reflector. 10. A series of small evenly spaced rivet holes 15 are drilled into the flange 14 infpositions to correspond with the holes 13 in flange 12 of the re-' fiector. v j

The reflector 10 and the front skin 11 are assembled into a structurally rigid unit by applying an adhesive to thefaces of flanges 12. andl4, joining the reflector 10. and front skin .11 and then inserting small rivets through each corresponding hole 13 and 1 51 of their respective unit'of the reflector assembly. Whenthusjoined along the two outer rims, the two oppositely. concave members provide .a' very rigid, andlight weight structure, .This

method of joining the reflector and the structural..mem berfhas been found to be very satisfactory but it is not to beconstrued as a limitation on this invention since' other .methodsfof. joining can be easiIydeVisedL The appearance of the reflector 1 0 and thefront-iskin ll thus assembled is further 'illustrated by the s'i'de elevation on reflecting surface for the waves transmitted by the an and polyester resin into the desired shape. The thickness of the reflector on completion is approximately .030" and the front skin 11 .030. In the process of building up reflector 10 to the desired thickness, a thin layer of aluminum or some other suitable metal may be sprayed in between the laminations of fiberglass to provide a good tenna feed. As a finishing step, both the reflector and the front skin may be painted with a suitable type of paint. Although specific materials and material thicknesses are mentioned above'with regard to constructing the reflector and the front skin, it will be appreciated that other materials or other combinations of materials and thicknesses maybe used. For example, the reflector can be stamped entirely from sheet aluminum and the front skin molded from the fiberglass and polyester resin with the respective skin thicknesses dependent upon the size of the reflector and the type of material.

A series ofsmall,

and below a horizontal plane.

Referring now particularly to Figures 2, 3 and 4, various features of the present invention are shown, such as the support for the reflector structure and the waveguide feed to the reflector. Reflector brackets 17 and 18, which may be likewise molded to the' desired shape from the fiberglass impregnated with polyester resin, are affixed to the backside of reflector 10, one on each side. BearingsZZ and 23, consisting of well known components, are fastened to the reflector brackets 17' and 18, respectively. Both bearing 22 supported by trunnion arm 19 and bearing 23 supported by trunnion arm 29 are mounted to be freely rotatable. The trunnion arms 19 and 20 are in turn fixed to a rotary table 21 which is arranged to be driven by a suitable mechanism (not shown) to provide 360 rotation or an oscillating motion as required.

Because the reflector is mounted to reflect a beam through a horizontal are determined by the rotary table mechanism as Well as to scan in a vertical are above and below a horizontal plane, it is necessary to mount the waveguide feed to the reflector to move with the reflector when scanning above and below a horizontal plane. Thus, the series of waveguide components to the reflector, designated by the numeral 24, are mounted at one end from one of the bearings and at the other end from waveguide support 28. In this instance, the waveguide components 24 are shown mounted from bearing 22. Supporting the waveguide components in this manner, the waveguide will move with reflector as it scans above Waveguide support 28 may also be molded from the fiberglass and polyester resin as may the reflector brackets and the reflector and structural member.

In order to complete the antenna transmission line, reflector 10 is provided with a circular cutout 16 to allow the waveguide feed 25 to the reflector to be inserted within the space defined by the oppositely concave components, reflector 10 and front skin 11. Waveguide 25, commonly termed the J horn because of its shape, connects at one end to the waveguide components 24. The loop of the J horn rests against a well defined, curved ridge 26 which extends across the width of front skin 11 and occurs at the deepest part of the concave form. Two bolts 27, welded to J horn 25, extend through holes drilled in front skin 11. By this means J horn 25 is bolted to front skin 11. This method. of simply and securely supporting J horn 25 provides a distinct improvement over the method of supporting prior art antenna structures, inasmuch as heretofore it has been necessary to construct the J horn from comparatively heavy material and to provide a three strut brace to prevent the J horn from vibrating from side to side as the reflector oscillates.

Although the present invention has been described in a specific embodiment, nevertheless various changes and modifications obvious to those skilled in the art are within the scope and contemplation of this invention. It will be apparent that many such changes can be made to the disclosed embodiment without departing from the basic concept taught herein of providing a structural member which can be attached to the front of the reflector.

What is claimed is:

1. An antenna assembly comprising a lightweight parabolic reflector consisting of a fibrous material impregmated with a resin, said reflector having a metallic layer therein and describing a peripheral flange, and a lightweight concave structural reinforcing member consisting of a fibrous material impregnated with a resin and having a peripheral flange, said flanges being joined together whereby said reflector and said member have their concave surfaces in opposed relation to define an internal cavity, waveguide means projecting through said reflector into said cavity and adapted to direct R. F. energy from a predetermined feed point toward said reflector, and one of said reflector and said member providing support means to maintain said waveguide means in a fixed position relative to said reflector.

2. An antenna assembly comprising a parabolic reflector consisting of a lightweight fibrous material impregnated with a resin, said reflector having a metallic layer therein and describing a peripheral flange, and a concave structural reinforcing member consisting of a lightweight fibrous material impregnated with a resin and having a peripheral flange, said flanges being joined together whereby said reflector and said member have their concave surfaces in opposed relation to define an internal cavity, waveguide means projecting through said reflector into said cavity and adapted to direct R. F. energy from a predetermined feed point toward said reflector, and said member providing means to maintain said waveguide means in a fixed position relative to said reflector.

3. An antenna assembly as defined in claim 2 wherein said fibrous material is fiberglass.

References Cited in the file of this patent UNITED STATES PATENTS 2,413,187 McCurdy -2 Dec. 24, 1946 2,415,678 Edwards Feb. 11, 1947 2,463,569 Smith Mar. 8, 1949 2,484,822 Gould Oct. 18, 1949 2,494,368 Steele et a1. Ian. 10, 1950 2,543,188 Moseley Feb. 27, 1951 2,679,004 Dyke et a1 May 18, 1954 2,747,180 Brucker May 22, 1956 

